1. Field of the Invention
The present invention relates to a photographing lens having an eccentricity adjusting device for adjusting the position of part of the lens groups constituting a photographing optical system in a plane orthogonal to an optical axis, in an adjustment operation during assembly of the photographing lens.
2. Description of the Related Art
This type of eccentricity adjusting device incorporated in a photographing lens is used to adjust the inclination of an image plane. Specifically, in digital cameras using a CCD image sensor on which object images are formed, it is required to adjust the inclination of the image plane with a higher degree of precision than conventional cameras using silver-salt film due to the characteristics of the CCD image sensor. The first lens group (frontmost lens group) of a photographing lens, which is positioned closest to the object side, is generally adopted as an eccentricity adjusting lens group for adjusting the inclination of the image plane. The inclination of the image plane can be adjusted by decentering the optical axis of the eccentricity adjusting lens group from the predetermined optical axis determined at the design stage of the photographing optical system.
However, if an eccentricity adjustment is made on the first lens group (eccentricity adjusting lens group), a problem with the amount of light on the image plane becoming uneven arises. If the brightness on the image plane becomes uneven, shading occurs in digital cameras using an image pickup device (CCD image sensor) on which object images are formed, which is undesirable.